A standard drill chuck has a body centered on and rotatable about an axis and formed with a plurality of axially extending angled guides angularly spaced about the axis. Respective jaws in these guides can be moved between a forward holding position in which they grip a tool and a rear releasing position. Screwthread formations on back edges of the jaws mesh with a threaded sleeve that is rotated relative to the chuck body to advance and retract the jaws. Alternately the guides are formed in a sleeve that rotates relative to the chuck body and the screwthread formations on the jaws mesh with a screwthread on the body for similar action.
Even though the jaws are made of steel, they are typically used to grip tools of similar hardness. Thus it is known to provide special hard-metal, e.g. carbide, inserts in the gripping faces of the jaws to reduce wear of the jaws and thereby prolong the life of the drill or lathe carrying the chuck. This is particularly the case for a hammer drill where the tool is also moved axially as it is rotated.
Such inserts must be mounted very, very solidly on the chuck jaw. Once installed they must be able to withstand considerable lateral forces as the chuck applies torque to the tool, and they must hold even when the entire tool gets fairly hot as is common in machining.
The typical chuck can hold a tool between 1.0 mm and 10.0 mm in diameter, and typically is set to go down to 0.8 mm so that when worn it can still hold a 1.0 mm bit. This can be done with standard chuck jaws by forming their front faces with a small groove, but the typical carbide insert is produced by sintering and cannot be given the desired shape, at least not with a groove of small radius of curvature. Thus it in not possible with insert-type jaws to provide the desired small clearance.